2018 Vermont State Hazard Mitigation Plan - Approved 11/17/18 4-4: Extreme Cold Potential Impact Hazard Impacts Probability Score*: Infrastructure Life Economy Environment Average: Cold 3 1 3 2 2 2 6 *Score = Probability x Average Potential Impact Extreme cold temperatures can have significant effects on human health and commercial and agricultural businesses, as well as primary and secondary effects on infrastructure (e.g. burst pipes from ice expansion and power failure). What constitutes “extreme cold” can vary across different areas of the country based on what the population is accustomed to in their respective climates. Exposure to cold temperatures can cause frostbite or hypothermia and even lead to heart attacks during physically-demanding outdoor activities like snow shoveling or winter hiking. When temperatures dip below freezing, incidents of icy conditions increase, which can lead to dangerous driving conditions and pedestrian-related slipping hazards. A large area of low pressure and cold air surrounding the poles, known as a polar vortex, is strengthened in the winter (Figure 44). When these polar vortex winds are distorted, due to cyclical strengthening and weakening or interaction with high-amplitude jet stream patterns, they have the potential to split into two or more patterns, allowing artic air to flow southward along a jet stream1. As this arctic air is able to access more southerly regions, extreme cold conditions can be observed in Vermont, which also have the potential to remain over the region for extended periods. The NOAA Wind Chill Chart identifies those temperatures and associated wind speeds that may cause frostbite if skin is exposed to the air over a certain period of time (Figure 43). Figure 43: Wind chill temperature index Source: NOAA 1 http://climatechange.cornell.edu/what-is-a-polar-vortex/ 97 SECTION 4: VERMONT PROFILE & HAZARD ASSESSMENT In anticipation of extreme cold temperatures, the National Weather Service may issue the following watches, warnings or advisories2, which are aimed at informing the general public as well as the agricultural industry: • Wind Chill Warning: Dangerously cold wind chill values are expected or occurring • Wind Chill Watch: Dangerously cold wind chill values are possible • Wind Chill Advisory: Seasonably cold wind chill values but not extremely cold values are expected or occurring • Hard Freeze Warning: Temperatures are expected to drop below 28°F for an extended period of time, killing most types of commercial crops and residential plants • Freeze Warning: Temperatures are forecasted to go below 32°F for a long period of time, killing some types of commercial crops and residential plants • Freeze Watch: Potential for significant, widespread freezing temperatures within the next 24-36 hours • Frost Advisory: Areas of frost are expected or occurring, posing a threat to sensitive vegetation In the fall, both abrupt cold snaps and record warmth can be observed, where the latter tends to be associated with southerly flow. Similarly, in winter, both extreme cold and record warm conditions occur, which can affect river flow (i.e. ice jam), snow cover, ground insulation and the agricultural industry. Figure 44: Wavy polar vortex configuration (left) versus more typical, compact configuration (right) Source: https://www.climate.gov/news-features/event-tracker/wobbly-polar-vortex-triggers-extreme-cold-air-outbreak 2 https://www.weather.gov/safety/cold-wind-chill-warning 98 2018 Vermont State Hazard Mitigation Plan - Approved 11/17/18 Extreme Cold History The winter of 1933–1934 was particularly cold, and the lowest temperature ever recorded for the State (-50°F) occurred at Bloomfield on December 30, 1933. Prior to this, extreme cold temperatures were widespread on January 4 and December 18, 1835, with -40°F at Montpelier and White River, -38°F at Bradford, -30°F at Rutland and -26°F at Burlington. Following the winter of 1933–1934, more than 20% of the apple trees in Vermont were eliminated, although this figure was less than 2% for the Macintosh variety. Temperature is a very important variable in promoting apple growth. The dwarf trees introduced in the 1860s lacked the winter hardiness needed to be truly viable in Vermont. The severe winter of 1917–1918 destroyed almost all of the Baldwin and other strains. Only the Macintosh variety survived, and it remains the dominant strain grown today. In 2001, temperature fluctuations in the spring produced a different loss. Daily maximum temperatures of at least 90°F followed by minimum temperatures near 20°F accelerated the flowering of the apple blossoms, which were then killed by the low nighttime temperatures. One of the most prolonged cold episodes lasted from January 18 to February 3, 1969. Maximum temperatures were below 0°F. Water mains and other connections froze and burst in record numbers across the State. Since then, extreme cold has been recorded in February 1993 and again on January 19, 1997. In both cases, cold dense air moving out from an Arctic high-pressure system caused temperatures to plummet. Daytime highs in 1993 were 10°F, while the minimums were -5°F. The winter of 1997 holds the record for longest streak of consecutive days below freezing, without a thaw, at 51 days. More recently, the winter of 2015 maintained below freezing temperatures for 27 days, while the period between December 24, 2017 and January 8, 2018 (or 16 consecutive days) did not exceed 32°F. Between the winters of 2000 and 2018, the number of recorded days per year with a daily temperature low of less than or equal to 0°F peaked during the 2015 winter at 31 days in Burlington, 44 days in Montpelier, 55 days in Island Pond and 32 days in Bennington. NOAA storm event history for Vermont includes several extreme cold/wind chill events since 2000, none of which included any deaths, injuries, or recorded damages: • January 17, 2000: A northwest wind averaging between 15-30 mph across southern Vermont, impacting Bennington and Windham Counties, with the addition of temperatures between 0°F to -10°F, produced dangerously low wind chill values of -50°F to -60°F. • January 25, 2007: An arctic cold front moved across Vermont on January 24, delivering very cold temperatures of 0°F to -25°F by the following morning. A secondary cold front accounted for the combination of brisk northwest winds of 10-15 mph and temperatures -5°F to -20°F with wind chill readings of -25°F to -40°F across the State. Another arctic front pushed across the area on January 29 and brought early morning low temperatures of -10°F to -30°F. • March 6-9, 2007: An arctic cold front swept across the State March 5 causing temperatures to plummet to -5°F to -20°F by dawn March 6. These frigid temperatures, accompanied by winds of 15-30 mph created dangerously cold wind chills of -20°F to -40°F. Brisk winds with temperatures around 0°F continued through the day. The winds subsided after sunset but it remained extremely cold through the morning of March 7. Arctic high pressure settled across New England March 9 with morning lows of -10°F to -34°F across Vermont. • January 14, 2009: An arctic cold front moved across Vermont which delivered some of the coldest temperatures across the region in several years as temperatures dropped over 20°F within several hours, averaging 20°F to 25°F below normal values, which were already at climatological winter minimums. 99 SECTION 4: VERMONT PROFILE & HAZARD ASSESSMENT Nighttime minimums were -10°F to -30°F across Vermont with isolated readings colder than -40°F. These extremely cold temperatures led to numerous cold weather related problems including numerous dead vehicle batteries and broken home/business water pipes. • January 23, 2011: Bitterly cold air settled into the region and temperatures plummeted to -10°F to -25°F below zero across southern Vermont in Bennington and Windham Counties. Brisk westerly winds diminished during the evening, becoming light and variable to calm after midnight, resulting in wind chill readings of -25°F to -35°F. • January 8, 2015: Wind chills colder than -25°F to -40°F were observed overnight January 7, with morning lows of -15°F to -35°F across Vermont, with the coldest temperatures within the southern Green Mountains and observed wind chills in the mountains from -40°F to -70°F. These dangerously cold wind chills lead to delayed school openings of 2 hours or cancelled classes on the morning of January 8. • February 15, 2015: An extremely frigid Arctic air mass pour into the region from the north, beginning during the late morning hours and a strong pressure gradient allowed for very strong winds. Northwest winds frequently gusted over 30 mph, with some gusts as high as 39 mph through the evening. Temperatures fell quickly through the day and dropped below zero for Sunday night into the morning of February 16. Some temperatures were as cold as -20°F with chill values of -20°F to -45°F, predominately in Bennington and Windham Counties. Many towns had warming shelters open and there were reports of bursts water mains and pipes due to the frigid temperatures. • February 13, 2016: Behind an Arctic cold front, very cold temperatures poured into the region upon brisk northwesterly winds, reaching lows of -12°F to -28°F along with winds gusting 20 to 40 mph, wind chill values reached -25°F to -45°F in Bennington and Windham Counties. • December 27, 2017-January 1, 2018: A frigid Arctic air mass poured into the region December 27 with gusty northwesterly winds. Low temperatures fell to as low as -5°F to -14°F with wind chill values as low as -37°F in Bennington and Windham Counties.